1. Field of the Invention
The invention relates to optical feedback systems, including beam monitors for acquiring information for adjusting the output of coherent beam sources or for processing interference data related to the characteristics of measuring beams. For example, measuring beam frequency and intensity information can be acquired from the measurement of phase variations apparent from other interference data. Particular applicability is found for use of the frequency and intensity information with the tunable sources of frequency-shifting interferometers.
2. Description of Related Art
Interferometers, particularly frequency-shifting interferometers, rely on assumptions regarding measuring beam frequency for interpreting interference information. For example, interference patterns are generally interpreted on a pixel-by-pixel basis by converting intensity information into modulo 2π phase offsets between the interfering portions of the measuring beam. The angular measures of phase are then converted into measures of distance as fractional portions of the measuring beam wavelength.
Frequency-shifting interferometers convert the intensity information of interference patterns into measures of distance by producing a succession of interference patterns at different measuring beam frequencies. Pixel intensity data fluctuates in accordance with the change in measuring beam frequency at different rates corresponding to the distance offset between the interfering portions of the measuring beam. Calculations generally assume that the succession of interference patterns are produced by evenly spaced measuring beam frequencies, and measurement accuracy depends upon the correctness of this assumption. Measurement accuracy also depends upon the assumption of an invariant overall intensity of the different measuring beams.